Stepped rod deck screen



April 14, 1970 P.YD. RANGER 3,506,122

STEPPED ROD DECK SCREEN Filed Dec. 6, 1968 M wmlm United States Patent O 3,506,122 STEPPED ROD DECK SCREEN Peter D. Ranger, Ville la Salle, Quebec, Canada, as-

signor to Allis-Chalmers Manufacturing Company, Milwaukee, Wis.

Filed Dec. 6, 1968, Ser. No. 781,752 Int. Cl. B07b 1/34, 1/12 U. S. Cl. 209--326 8 Claims ABSTRACT OF THE DISCLOSURE A vibrating screen is disclosed having a deck made up of parallel rods spaced to pass therebetween particles smaller than a predetermined size. Each rod is a continuous piece shaped to define, in operating position, a descending flight of at least several steps each transverse to the rods with each step comprising a tread and a riser. Each riser is shorter than the treads and sloped to define an angle of declination substantially steeper than adjacent treads and the angle of the riser below a horizontal plane through a top portion thereof and toward the lower end of the flight, is at least about 70 degrees. A transverse tie rod is arranged beneath the deck at or close to the upper end of each tread, and preferably the tie rod is not farther from the upper end of the tread than approximately /2 of the vertical drop established by the riser connected to the upper end of the tread. A predetermined number of the steps, comprising less than half of the steps, and beginning with the top step, are provided with a steeper downward slope than the remaining steps of the flight to provide particles descending the deck with an initial velocity and momentum for free flight trajectory over risers and provide a cluster disrupting impact landing of such particles on the upper end of each tread downwardly and beyond the tie rod beneath the upper end of each tread.

CROSS REFERENCE T RELATED PATENT APPLICATION This application discloses an invention applied to a vibrating screen which is also the subject of my copending United States patent application entitled Rod Deck Screen With Resilient Material Receiving Section, Ser. No. 7 81- 811, filed concurrently with this application.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to material separating screens and in particular to a deck for a vibrating screen adapted to size agglomerates of sticky material such as green pellets of iron ore discharged from balling drums for drying and heat hardening into pellets that are a desired charge material for a blast furnace.

Description of the prior art US. Patents 2,750,272 of 1956; 2,925,336 of 1960; and 3,235,372 of 1966 are examples of iron ore pellet heat hardening systems which in commercial installations are provided with vibrating screens for sizing green pellets discharged from balling pans or drums for heat hardening in furnace assemblies.

It has been long known that screens having metal or textile cloth decks, that is decks of perforated plates or decks woven of metal or textile threads, are more likely to plug when screening damp sticky materials than are screens having decks of parallel rods extending in the direction of material flow. From as early as US. Patent 444,252 of 1891, heavy duty rod deck screens were known having steps defined by end to end and parallel rods but 3,506,122 Patented Apr. 14, 1970 with alternate portions projecting upwardly that resulted in material being treated far too roughly for such a screen to be used to size water bound agglomerates of finely divided mineral ore. Later developed screens such as shown in US. Patent 2,636,607 of 1953 are disclosed as having a rod deck assembly that handles fragile agglomerates much more gently and in which each strand is made up of several rods arranged approximately end to end. With such screens, however, sticky material tends to collect and build where such end to end rod segments meet. Later patents such as US. Patents 2,914,177 of 1959; 3,037,630 of 1962 and 3,289,837 of 1966 disclosed screen decks in which each strand is a single continuous piece. But screens built according to these teachings have resulted in some undesired clustering of water bound agglomerates and an accumulation of the finely divided mineral ore at locations where transverse tie rods or other support structures pass beneath the screening surface. Such accumulations act as dams that interfere with desired flow of material down the sloped screen deck and limit or reduce the capacity of the screen.

SUMMARY OF THE PRESENT INVENTION It is an object of the present invention to provide a new and improved screen with a deck of single piece rods defining a downwardly flight of steps that impart to pellets being sized, a free light trajectory over transverse tie rods passing beneath the deck to avoid an undesired accumulation of screen binding material gathering about portions of such tie rods exposed between rods of the screen deck.

Another object of the present invention is to provide a new and improved vibrating screen with a deck of single piece rods defining a downward flight of steps that impart to pellets being sized, a free flight trajectory from one tread to the next lower tread and provide a cluster disrupting impact landing of pellets on a tread of a lower and adjacent step.

According to a preferred embodiment of the present invention for achieving such objects, a descending flight of steps is formed by rods parallelly spaced apart and extending in the direction of descent. Each step is defined by a tread and riser portion formed in each rod, and each rod defines at least a plurality of steps. Each riser is sloped to define an angle of declination much steeper than the downward slope of the adjacent treads, and the slope of the riser defines an angle below a horizontal plane from the top of the riser toward the lower end of the flight, of at least about 70 degrees. Transverse tie rods, which are necessary to hold the assembly together, are located to be beneath a free flight trajectory of pellets coming down the flight of steps and air hourne over each riser. The location for'such tie rods is beneath the deck and not farther from the upper end of the tread than about /2 of the vertical drop provided by riser connected to the upper end of the tread. The first few steps, preferably the first three, have a steeper downward slope than the following steps to impart to pellets landing thereon the desired velocity and momentum down the flight of steps, for the desired free flight trajectory over risers and thereby provide a flight and a cluster of disrupting impact landing of such pellets on the upper end of each lower tread and downwardly of the tie rod beneath each tread upon which they land.

Other objects of the invention and how they are attained will appear from the following description of the invention with reference to the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevation of a vibrating screen according to the present invention, with a portion of the screen body broken away to show the configuration of the deck and certain deck supporting structures;

FIG. 2 is a partial view of the screen shown in FIG. 1, taken along the line IIII in FIG. 1 as viewed in the direction indicated by the arrows;

FIG. 3 is an enlarged fragmentary view of a portion of a rod that according to one embodiment of the present invention forms part of the deck in the screen of FIGS. 1 and 2; and

FIG. 4 is an enlarged fragmentary view, similar to FIG. 3 but of a second embodiment of the present invention.

Referring to FIG. 1 a vibrating screen 1 is shown comprising support base members 2 and a screen body frame 3 resiliently mounted on the base 2 and inclined in the conventional manner. The screen body 3 is supported on base 2 and is vibrated relative thereto by an assembly 4 including a vibrator 5, all of which may be constructed and arranged in the manner described in US. Patent 3,030,098 of 1962.

Referring to FIGS. 1 and 2, the screen 1 is provided with a deck assembly 10 made up of parallel rods 11 spaced apart from each other to define therebetween a space 12 for passing particles 13 which are smaller than a size predetermined by the space 12 between rods 11 and for guiding along the tops of the rods 11, particles 14, which are larger than space 12. Each rod 11 is a single continuous piece shaped to individually and collectively define a descending flight of steps 15 transverse to rods 11. Each step 15 comprises a tread 16 with a riser 17 between adjacent treads 1,6.

The rods 11 are supported by transverse tie rods 20 each of which, as shown in FIG. 2, is carried by arms 21, 22 connected to a cross arm 23 by bolts 24. Flanges 25 and 26 on the ends of each cross arm 23 are connected by bolts 27, 28 to the opposite sides of the screen body 3.

Referring to FIG. 3 a pair of adjacent treads 16a, 16b and riser 17 therebetween, according to one embodiment of the present invention, is shown to an enlarged scale. The riser 17 is sloped to define an angle of declination A below a horizontal plane 30 substantially steeper than the downward slope of the adjacent treads 16a and the angle A is substantially larger than the angle of declination B of tread 16a below plane 31. As shown in FIG. 3 the angle of declination A of riser 17 below plane 30 is at least about 70 degrees while the angle B, even for the steepest steps 15a, is not more than 50 degrees. The transverse tie rod 20 shown in FIG. 3 is adjacent the upper end 32 of tread 16b and preferably not farther therefrom than about one half of the vertical drop X provided by riser 17.

FIG. 4 shows another embodiment of the present invention in which the angle of declination A of the riser 17' is much steeper than the corresponding angle of riser 17 in FIG. 3, and the angle of declination A of riser 17 below a horizontal plane 30 is greater than 90 degrees. A tie rod 20" in FIG. 4, similar to rod 20 in FIG.3, is arranged beneath tread 16b adjacent its upper end 32', and preferably not further therefrom than about one-half of the vertical drop X' provided by riser 17'.

Referring again to FIG. 1 the first few steps 15a, 15b, 15c, 15d beginning at the receiving end and on the upper end of the deck 10 from vibrator provides a first and material receiving section for receiving material particles 13, 14 which may be such as green pellets of finely divided iron ore. The treads of these steps 15a-15d have a substantially steeper downward slope than the steps downwardly thereof, to provide the particles 14 with initial velocity and momentum needed in order that the screen will operate in the manner that will hereinafter be described.

In one preferred design of a screen according to this invention for operation is a system such as described in US. Patent 3,235,372, to size green waterbound pellets of finely divided iron ore, the base 2 will be arranged to support the screen body 3 with a downward slope from horizontal of about 10-20 degrees. Rods 11, A inch diameter may be spaced apart about 0.6 inch to size pellets at about inch, which is a desired size for use in systems of type referred to. The first few steps Isa-15d, which define a material receiving zone, may be provided with treads 16 sloping downward from horizontal in a range from about 50 degrees at the beginning of the receiving zone to perhaps as little as about 15 degrees where the receiving zone ends and the material outrun portion, defined by the steps downwardly thereof, begins. With steps provided as shown in FIG. 3 or FIG. 4, the discharge of clusters of pellets is avoided as the pellets coming down such a sloped deck will have velocity and momentum to become air bourne with a free flight trajectory over the risers 17, 17' and transverse tie rods 20, 20 and provide an impact landing that will disrupt any clusters that are formed of the particles 14. This impact landing on each tread 16 is on the upper end of each tread but downwardly of the tie rod 20 beneath the tread. Thus any fines that are loosened from the agglomerates 114 can fall freely through space 12 without making contact with tie rod 20 and thus a tendency of fines to build a dam over tie rods that impedes pellet flow down the screen, is also avoided by the present invention.

A test was performed to determine the increased capacity of a vibrating screen provided with a deck according to the present invention. A screen was chosen having spaced rods arranged lengthwise to the screen body and having a downward slope but without steps according to the present invention. The capacity of the screen was 60 tons per hour. A deck according to the present invention was then substituted. The new deck had the same number of rods, the same rod diameter, the same spacing between rods but defined steps according to the present invention. The capacity of the screen for the same material, was increased :from 60 tons per hour to tons per hour.

From the foregoing detailed description of the present invention, it has been shown how the objects of the invention have been attained in a preferred manner. [However, modifications and equivalents of the disclosed concepts such as readily occur to those skilled in the art are intended to be included within the scope of this invention.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A deck assembly for a vibrating screen comprising:

(A) a plurality of deck rods parallelly spaced apart in fixed position by a plurality of transverse tie rods connected to the underside of the deck rods, and the deck rods shape to define a flight of at least a plurality of descending steps having an upper particle receiving end and a lower particles discharging end;

(B) each of the rods and the steps defined by the rods having a tread portion and a riser portion;

(C) a first section of the deck for receiving particles to be screened, defined by a predetermined number of steps beginning at the upper end of the flight of steps, and the treads of the steps of the first section having a downward slope steeper than treads of steps downwardly of the first section;

(D) each riser of at least the first section having a slope defining an angle of declination below a horizontal plane through the top thereof and toward the discharge end of the deck, that is greater than the angle of declination for the tread connected to the top thereof, to provide for particles that move downwardly on top of each such tread, a free flight trajectory over the downwardly adjacent riser and a cluster disrupting impact landing on the next tread downwardly thereof; and

(E) the tie rods being arranged beneath at least the first section of steps to provide a tie rod downwardly of each riser with such tie rod located beneath the adjacent upward end of the next downward tread and not farther from the upper end of the tread beneath which such tie rod is located than approximately onehalf of the vertical drop over the riser connected to the upper end of such tread, to thereby place each such tie rod beneath the free flight trajectory of particles over such a riser.

2. In an assembly according to claim 1, the angle of declination of each riser of at least the first section being at least about 70 degrees.

3. In an assembly according to claim 1, the angle of declination of each riser of at least the first section being greater than 90 degrees.

4. An assembly according to claim 1 in which each riser in the entire deck assembly has a slope defining an angle of declination that is greater than the angle of declination for the tread connected to the top thereof and each tie rod in the entire deck assembly being not farther from the upper end of the tread beneath which such tie rod is located, than approximately one-half of the vertical drop over the riser connected to the upper end of such tread.

'5. A vibrating material separating screen comprising:

(A) a pair of parallel frame members spaced apart from each other;

(B) a plurality of parallel deck rods supported between the frame members and parallel thereto, with the rods spaced apart to define a deck with a particle receiving end at a first elevation, passages between adjacent rods for passing particles smaller than a predetermined minimum size and for guiding along the top of the rods particles larger than the predetermined minimum size, and a particle discharging end at a second elevation lower than the first elevation;

(C) each of the deck rods being a continuous piece having a shape that individually and collectively define a series of descending steps comprising a plurality of alternate treads and risers;

(D) a vibrator mounted between the frame members transverse to the deck rods and intermediate the ends thereof and operative to impart reciprocating motion to the rods in a vertical plane parallel to the rods;

(E) a first section of the deck for receiving particles to be screened defined by a predetermined number of the steps being at the particle receiving end of the deck and with the treads of the steps of the first section having a steeper downward slope than the treads of steps downwardly thereof;

(F) each riser of at least the first section having a slope defining an angle of declination below a horizontal plane through the top thereof andtoward the discharge end of the screen, that is greater than the angle of declination for the tread connected to the top thereof, to provide for particles coming down each such tread a free flight trajectory over the downwardly adjacent riser and a cluster disrupting impact landing on treads downward thereof; and

(G) the deck rods being supported by a plurality of transverse tie rods connected to the underside of the deck rods, the tie rods being arranged beneath at least the first section of steps to provide a tie rod downwardly of each riser with such tie rod located beneath the adjacent upward end of the next downward tread and not farther from the upper end of the tread beneath Which such tie rod is located, than approximately one-half of the vertical drop over the riser connected to the upper end of such tread to thereby place each such tie rod beneath the free flight trajectory of particles over such a riser.

6. In an assembly according to claim 5, the angle of declination of each riser of at least the first section being at least about degrees.

7. In an assembly according to claim 5, the angle of declination of each riser of at least the first section being greater than degrees.

8. An assembly according to claim 5, in which each riser in the entire deck assembly has slope defining an angle of declination that is greater than the angle of declination for the tread connected to the top thereof and each tie rod in the entire deck assembly being not farther from the upper end of the tread beneath which such tie rod is located, than approximately one-half the vertical drop over the riser connected to the upper end of such tread.

References Cited UNITED STATES PATENTS 545,106 8/1895 Spicer 209-393 X 2,636,607 4/1953 Roubal 209-395 2,914,177 11/1959 Parks 209-396 3,030,098 4/1962 Roubal 209-326 X 3,307,698 3/1967 Hatfner 209-344 X FRANK W. LUTTER, Primary Examiner U.S. Cl. X.R. 209-395 

